Ptychographa, a Lichen Genus New to North America

Abstract

The genus Ptychographa is reported in North America from Oregon and Washington. Ptychographa xylographoides Nyl. is a lirellate crustose lichen that occurs exclusively on decorticate wood. The species is characterized by a dark brown to black exciple, simple spores, and a hymenium that is partitioned lengthwise. It grows at all levels in the canopy in old-growth conifer forests in the Cascade Range and has also been found on coarse woody debris in younger forests. Ptychographa xylographoides Nyl. is a lirellate crustose lichen that occurs exclusively on wood. This species has been found in coniferous forests in western Oregon and Washington. Originally it was found from the gondola suspended by the Wind River Canopy Crane, a large construction crane installed in an old-growth forest at T. T. Munger Research Natural Area. An ongoing study with Roger Rosentreter, Jeanne Ponzetti, and Dave Shaw disclosed that this species is fairly frequent on dead in the canopy. The species had previously been reported only from the British Isles. The local material matches the description in the British flora (Purvis et al. 1992, p. 514) in most details. The substrate in Great Britain is apparently more restrictive than in the Pacific Northwest. Purvis et al. (1992) reported it on wood of ? horizontal surfaces of fallen trees, while we found it on both vertical and horizontal at all levels in the canopy. Superficially Ptychographa appears similar to some local Opegrapha species, forming jet black, elongate apothecia. Anatomically it is quite distinct however. Ptychographa has simple colorless spores in contrast to the multiseptate spores of Opegrapha. Furthermore, the hymenium of Ptychographa is usually divided by a longitudinal ridge of dark, sterile tissue (Figs. 1, 2). These lengthwise divisions of the hymenium are most easily seen in transverse section (Fig. 2), but I have found it to be a useful hand-lens character for field identification. Look for an extra fold or ridge between the two marginal ridges of exciple (Fig. 1) Xylographa, while sharing the simple spores of Ptychographa, is easily separated by its pale excipie, in contrast to the dark, carbonaceous exciple of Ptychographa. Although the exciple of Xylographa can be dark when viewed with a handlens, a thin section under the compound microscope will always reveal a pale inner exciple, even when the surface is dark. Furthermore, Xylographa lacks the distinctive bands of sterile tissue found in Ptychographa. The thallus of Ptychographa is inconspicuous, usually consisting of minute brownish granules (containing the green photobiont) that are widely scat ered on a whitish background. The granules are